Conventional micro-electro-mechanical system (MEMS) products combine two chips into a single integrated package. This two-chip packaging approach includes, for example, one chip that includes the MEMS device or structure (mechanics) and one chip that includes the associated electronics, and the two chips are included in one single package. The two dies that include each of the MEMS and the electronics are connected via wire bonds. The reasons for the two-chip approach include difficulties in monolithically integrating the two components (MEMS and electronics), and the ability to separately optimize the MEMS device and the electronics in order to get the optimum overall yield.
FIG. 1 shows a block circuit diagram of a conventional MEMS device 100, under the prior art. This conventional MEMS device 100 includes a MEMS 110 (e.g., MEMS die) connected to associated electronics 120 (e.g., electronics die). The MEMS 110 is a capacitive accelerometer in which acceleration results in deflection of a movable mass. The deflection to which the package is subjected also results in capacitive changes in the MEMS 110, and the capacitive changes can be sensed by the electronics 120. The sensing capacitors C_S1 and C_S2 of the MEMS 110 change according to the acceleration experienced thereby introducing changes in the signal measured by the electronics. The bond wires 130 that connect the MEMS 110 to the electronics 120 form parasitic capacitances C_PB1 and C_PB2 that are modeled in parallel to the sensing capacitors C_S1 and C_S2. If the bond wires 130 do not change their position and the dielectricum between the bond wires 130 stays constant, the bond wires 130 only add constant capacitances to the sense capacitors. This leads to an offset in the system 100, and conventional systems calibrate for this offset by subtracting a constant value from the output signal of the system.
However, changes in the distance of the bond wires or the dielectric between the bond wires as a result of temperature changes and system age can make accurate system calibration difficult. The parasitic capacitances C_PB1 and C_PB2 being connected in parallel to the sensing capacitors C_S1 and C_S2 make it difficult in conventional systems to adequately compensate or calibrate for the offset drift in the parasitic bond capacitances C_PB1 and C_PB2 resulting from temperature variances and aging. For example, the distance of the bond wires in molded packages changes because of the thermal expansion coefficient of the molded mass of the system, and these changes in distance introduce changes in the parasitic capacitances C_PB1 and C_PB2.
Conventional MEMS systems are unable to compensate for the change of these parasitic capacitances because it is impossible to predict in which direction the bond wires will be deflected. Furthermore, a change of the dielectric between the bond wires (e.g. because of humidity) also introduces changes in the parasitic capacitances C_PB1 and C_PB2. The uncompensated variable offset due to the change of the dielectric between the bond wires can be a major obstacle for new applications of the MEMS (e.g., automobile hill hold control, automobile alarm, etc.). Consequently, there is a need for systems and methods that control the coupling or connection of the MEMS die to the electronics die to eliminate or cancel errors introduced by the bond wire in an output of the MEMS die.